The present invention relates to a ceramic body based on aluminum titanate that has improved properties for use in high temperature applications and a method for making the same. In particular, the present invention relates to a ceramic body having a crystal phase of aluminum titanate or aluminum titanate-mullite and a glass phase of alkali or alkaline earth aluminosilicate, and exhibiting a high resistance to thermal decomposition and low thermal cycling growth or change in dimensional integrity.
Aluminum titanates have been proposed for use in high temperature applications, as diesel particulate filters and substrate for catalytic converters, an example of which is known commonly in the art as a honeycomb substrate. Additionally, aluminum titanates are desirable in applications where the thermal shock resistance and the ultimate use temperature are high. Cellular substrates used under conditions of high thermal gradients are examples of this application. Typically, structures such as these are subjected to harsh environments which require high thermal shock resistance, low thermal expansion, and good mechanical properties. Furthermore, the ceramic material must maintain these desirable properties after prolonged exposure at high temperatures, without significant change in dimensional integrity with repeated cyclings in the desired temperature range.
It is known in the art that aluminum titanate undergoes decomposition into alumina and titania with prolonged exposure to high temperatures, and that the inclusion of rare earth oxides and iron oxides provides stability under continuous high temperature use (U.S. Pat. Nos. 4,483,944 and 4,855,265). However, the biggest challenge with honeycomb substrates comprising aluminum titanates is thermal cycling growth or dimensional change with repeated cycling at high temperatures. U.S. Pat. No. 4,767,731 teaches that in a mullite-aluminum titanate ceramic improved durability against thermal cycling is obtained by maintaining the glass phase of less than 5%.
It has been found with the present invention that the addition of surprising large amounts of glass to an aluminum titanate-based ceramic has beneficial effects on thermal cycling growth while the addition of Fe2O3 to form Fe2TiO5 phase as the stabilizer in aluminum titanate, unless minimal, exacerbates this condition. The combination of aluminum titanate and alkali or alkaline earth aluminosilicate glass may then be subsequently extruded and sintered to form a honeycomb structure. The resultant structure produces a product with reduced thermal cycling growth and good thermal durability.